The present invention is directed to a combination of solubilizing agents and defoamers that are used in conjunction with a dispersant for cementitious compositions to control air contents in cementitious compositions. Particularly, the present invention is directed to a combination of solubilizing agents with water insoluble defoamers that are used in conjunction with dispersant for cementitious compositions to control air contents in cementitious compositions.
Hydraulic cements, such as Portland cement, are used to form structural formations. Hydraulic cements can be mixed with aggregate to form mortars, which additionally include small aggregate and water, or concrete, which are mortars which additionally include large aggregate.
When working with hydraulic cements, it is desired to increase the slump properties of the initially formed hydraulic cement composition to aid in placement of the composition and to extend the period of flowability in order to provide working time to finish the placement of the structure. Admixtures can be added to hydraulic cement that increase the slump. Additionally, admixtures can be added that also reduce the amount of water required and to produce flowable cementitious compositions. The reduced water content increases the strength of the resulting hydraulic cement formation.
One admixture for increasing the flowability and reducing the water content is a polycarboxylate dispersant. Polycarboxylate dispersants are polymers with a carbon backbone with pendant side chains, wherein at least a portion of the side chains are attached to the backbone through a carboxyl group or an ether group. Polycarboxylate dispersants are very effective at dispersing and reducing the water content in hydraulic cements.
One drawback to polycarboxylate dispersants is that they have a tendency to entrain air in the cementitious composition during mixing While some entrained air may be desired for particular applications, such as providing freeze-thaw durability to the cement, an excess of entrained air is detrimental to the compressive strength of the resulting hydraulic formation.
Generally in the construction industry, non-air entrained cementitious compositions having an air content of less than 3% is desired, with an air content of less than 2% being preferred. Air entraining admixtures are sometimes used to provide purposeful air contents of 5-8% which improves the freeze thaw durability of the cementitious mixture. When this is the case, it is desirable to be able to adjust the air content by changing the air entrainer dosage and to have the resulting air remain stable over time.
To overcome the excess entraining of air in cementitious compositions, defoamers have been added to the cementitious mix to reduce the air content to a desired level. Defoamers typically have been included with the polycarboxylate admixture. However, the defoamers used in the prior art have been non-water-soluble compositions used alone. The problem with non-water-soluble defoamers is that they give an inadequate long term storage stability to the admixture resulting in phase separation. The polycarboxylate dispersant is generally a water soluble dispersant. When a non-water-soluble defoamer is used in conjunction with a water soluble dispersant, the mixture separates over time. This requires that the mixture be mixed prior to use. Also, some insoluble defoamers can cause unpredictable air contents over time.
Commercial defoamers typically contain a mixture of materials. The major part is an oil or organic liquid (up to 95 parts by weight), small particulate (up to 15 parts by weight), and a surfactant (up to 5 parts by weight).
Another technique used in the prior art has been the grafting of the defoamer onto the dispersant molecule.
The prior art, however, has not shown the combination of a defoamer that is not chemically combined with the polycarboxylate dispersant that is used in conjunction with a solubilizing agent.
What is needed in the industry is a combination of a water insoluble defoamer, a dispersant for cementitious compositions, and a solubilizing agent that solubilizes the water insoluble defoamer that produces controllable air contents in non-air entrained and air entrained cementitious compositions.
It is therefore an object of the invention to provide a combination of a water insoluble defoamer, a dispersant for cementitious compositions, and a solubilizing agent that solubilizes the water insoluble defoamer that produces controllable air contents in non-air entrained and air entrained cementitious compositions.
It is another object of the invention to provide an admixture containing a dispersant for cementitious compositions, a solubilizing agent, and a water insoluble defoamer that is stable over time.
Solubilizing agents can be combined with water insoluble defoamers and dispersants for cementitious compositions to provide an admixture for cementitious compositions that is stable over time. The resulting admixture has long term storage stability so that the admixture does not need to be mixed prior to use at the work site.
The present invention provides an admixture for cementitious compositions comprising a water insoluble defoamer, a dispersant for cementitious compositions, and a solubilizing agent that solubilizes the water insoluble defoamer.
The present invention also provides a cementitious composition comprising cement, water, a water insoluble defoamer, a dispersant for cementitious compositions, and a solubilizing agent that solubilizes the water insoluble defoamer.
The present invention also provides a method of making a cementitious composition comprising mixing cement, water, a water insoluble defoamer, a dispersant for cementitious compositions, and a solubilizing agent that solubilizes the water insoluble defoamer.